A hybrid vehicle has received attention as an environmentally friendly vehicle. In addition to a conventional internal combustion engine, the hybrid vehicle is equipped with a power storage device, an inverter and an electric motor driven by the inverter, as power sources for the vehicle to run.
Japanese Patent Laying-Open No. 9-168206 discloses such a hybrid vehicle in which necessary regeneration energy can be recovered to a battery in any running state. In this hybrid vehicle, a detection signal of a battery capacity, a signal indicative of an expected running state from a navigation system and a signal indicative of an actual vehicle running state are received as input signals to control the battery capacity to be constantly close to a target amount of charge α while ensuring charging energy (100−α) for regeneration. A driver is allowed to manually set the target amount of charge α.
According to this hybrid vehicle, the battery capacity is controlled in comparison with the target amount of charge α, which allows necessary regenerative energy to be recovered to the battery in any running state.
Recently, a great deal of attention has been given to a hybrid vehicle in which an on-vehicle power storage device can be charged from a power source outside the vehicle. Such an externally rechargeable hybrid vehicle may be equipped with a power storage device having a power storage capacity larger than that of a conventional hybrid vehicle (a hybrid vehicle lacking the external rechargeability) for the purpose of making use of the advantage of charging from the external power source, and may mostly run using solely an electric motor.
However, when applying the technique disclosed in the aforementioned Japanese Patent Laying-Open No. 9-168206 to the externally rechargeable hybrid vehicle, setting the target amount of charge α at a great value may cause the engine to start without sufficiently utilizing charged electric power supplied from the external power source, so that effective utilization of energy is less likely to be fully achieved. Setting the target amount of charge α at a great value will cause the state where the amount of charge of the battery is large to continue. Such state where the amount of charge is constantly large will result in degradation of the battery.
When the user is allowed to set a system state, the setting made by the user may be canceled due to insufficient conditions depending on a vehicle state. Even in such a case, it is desirable for the sake of convenience to hold the setting made by the user, and to bring about the state set by the user once the conditions are satisfied.